Sindi Maduhu

Sindi Maduhu


Tanzania Petroleum Development Corporation (TPDC)


SESSION 5:  Prospective Basin Architecture revealed in the Eyasi Wembere Block by recent Airborne Gravity Gradiometry and Aeromagnetic Survey

Sindi Maduhu, Asiadi Mrutu & Kelvin Komba

The Eyasi-Wembere basin is among the asymmetrical, extensional rift basins that have developed along the eastern arm of the East African Rift System (EARS). The basins formed within the Tanzanian Craton on the west and the north-south trending Mozambican Mobile Belt to the east, as a direct consequence of the divergence of the Nubian, Somalian and Arabian plates. The block have four identified sub-basins: Western (Wembere and Manonga depresion), Central (Lake Eyasi), Northeast (Manyara) and Natron each of which can be sub-divided into fault-bounded compartments. Similar to other Neogene basins of the EARS, they are characterized by complex extensional and compressional structures such as thrust faults, steeply dipping normal faults, full and half-grabens. The basin started forming after breakup of Gondwana that began along what is now the eastern coastline followed by Volcanism in the vicinity of the Tanzanian Divergence started in the Early Pliocene. A second major volcanic phase occurred, associated with renewed extension along the rift faults.

Stratigraphy of the sedimentary deposits in the rift basin still unknown due to lack of exposure of rocks. A thick volcanoclastic sediments and fluvial-lacustrine sediment may be overlying potential reservoir and source rocks in the area.

The Eyasi-Wembere basin has approximate area of 1800 km2 and has no seismic coverage or wells. Legacy aeromagnetic and limited ground gravity data suggest the presence of suitably thick sediments in places. In order to target and optimize future seismic surveys an airborne gravity gradiometry (AGG) and magnetic survey was conducted over the entire block. The same exploration strategy was successfully employed, for example, for the N. Turkana basin (Kenya) and Lake Albert (Uganda).

Integrated interpretation of the survey results has mapped and modeled the main depocentres, key boundary structures and internal basin faulting and blocks. Priority areas with deep sediments for further exploration/detailed follow-up and seismic surveys are clearly defined. The depth of sediments in the identified areas are deeper enough for oil generation and accumulation.